Petr Drkula is mostly famous for his (usually long) conceptual algorithmic compositions. These are often formed by pulsations that unabrubtly variate to put you either in a kind of meditative or really concentrated state, according to your context and your attention ratio between the music and everything else (inside and outside). But Petr is also composing for and performing on different classical acoustic instruments. And also using his voice.
For "Lullabies for adults" he drew inspiration from the moravian/silesian folk songs of his ancestors. He performed ballads, narrative songs and lullabies a lot. Then he recorded an entirely acoustic album for viola and voice. In the course of making of the tracks he hasn't had focused on any specific sound or structural idea though. He just took a viola and sang and played, the improvisation being influenced, of course, and containing elements of the folklore he used to play. The ballads, narrative songs and lullabies - the album is a Petr Drkula acoustic distillation of these musical forms.